package com.zdy.demo;

import java.util.Arrays;

/**
 * 06. 题目
 * 由前序和中序遍历重建二叉树
 * 题目描述：输入某二叉树的前序遍历和中序遍历的结果，请重建出该二叉树。假
 * 设输入的前序遍历和中序遍历的结果中都不含重复的数字。例如输入前序遍历序列
 * {1,2,4,7,3,5,6,8}和中序遍历序列{4,7,2,1,5,3,8,6}，则重建二叉树并返回
 * @author deyou
 * @version 1.0
 * @date 2021/5/21 7:53
 */
class TreeNode{
    int val;
    TreeNode left;
    TreeNode right;
    TreeNode(int val){
        this.val = val;
    }
}
public class BinaryTreeSearch06 {

    public static TreeNode reConstructBinaryTree(int[] pre, int[] in) {
        if (pre == null || in == null || pre.length == 0 || in.length == 0)
        {
            return null;
        }
        if (pre.length != in.length) {
            return null;
        }
        TreeNode root = new TreeNode(pre[0]);//由前序遍历的第一个元素找到根节点
        for (int i = 0; i < pre.length; i++) {
            if (pre[0] == in[i]) {
                //左子树递归调用
                root.left = reConstructBinaryTree(Arrays.copyOfRange(pre, 1,
                        i + 1), Arrays.copyOfRange(in, 0, i));
                //右子树递归调用
                root.right = reConstructBinaryTree(Arrays.copyOfRange(pre,
                        i + 1, pre.length), Arrays.copyOfRange(in, i + 1, in.length));
            }
        }
        return root;
    }

}
